1. Field of the Invention
This invention relates to a heating apparatus for locally heating fuel oil in a fuel storage tank installed on the ground to reduce viscosity of the fuel oil so that the fuel oil may be drawn out of the tank with small power, or in a fuel storage tank installed, for example, on a ship to heat the outgoing fuel oil to a temperature suited to combustion as well as to enable the fuel oil to be drawn out of the tank and fed to the engine with small power.
More particularly, this invention relates to a heating apparatus for heating liquid stored in a tank comprising a hollow member disposed substantially horizontally in the tank, and a heater housed in the hollow member and extending substantially over an entire length of the hollow member, the hollow member including inlet means to permit entry of the liquid into the hollow member and outlet means to permit exit of the liquid from the hollow member after the liquid is heated by the heater.
2. Description of the Prior Art
A known example of this type of heating apparatus is disclosed in Japanese Patent Publication No. 29-8136. To describe its construction roughly, a hollow member containing a heater is closed at one longitudinal end and open at the other to let in liquid. This hollow member is horizontally inserted into the tank, penetrating a side wall thereof, and includes an opening adjacent the other end thereof and outwardly of the tank to let out heated liquid.
Such a heating apparatus has the following disadvantages:
(a) The liquid flows in one direction within the hollow member from the inlet opening at one end to the outlet opening adjacent the other end, and gets gradually heated to a high temperature during the one-way flow. The liquid within the hollow member, therefore, has an increasingly less temperature gap with the heater toward the deep end or the other end of the hollow member. In other words, the heater produces a temperature characteristic curve rising sharply adjacent the inlet opening but levelling off with a worsening heat exchange rate toward the outlet opening. Thus it can be said that the prior art apparatus includes heat exchange regions having a poor temperature rising characteristic. That is to say the entire length of the heater is not utilized for effective heat exchanges. Therefore, in order to heat the outgoing liquid to a desired temperature it is necessary to increase the heater in length, number or power.
(b) The end of the hollow member where the liquid outlet opening is provided in the part that gets hottest. But since this part is located outwardly of a side wall of the tank, considerable energy loss occurs owing to heat radiation to the ambient.
(c) Since the hollow member communicates with the tank interior only through the inlet opening at one end thereof, the liquid within the hollow member may become overheated when there is no or only little liquid allowed to leave the hollow member through the outlet opening. This is because this known apparatus provides a low exchange rate between the hot liquid within the hollow member and cold liquid outside in the tank.